High capacity and reliability secondary (rechargeable) electrochemical cells and batteries are pivotal to improving mobile electronics, and are becoming more important in transportation and energy storage applications as batteries take on more prominent roles in these realms. Key chemistries in current commercial secondary cells, and the batteries constructed from those cells, include Li-ion, lead-acid (Pb-acid), nickel-metal-hydride (NIMH), and Zn-air.
Mg based secondary cells, whether based on metal or other electrode types, are now emerging as a potential improvement upon existing cell types for increased gravimetric and volumetric energy-density. Mg cells are expected to approach 500 Wh/Kg versus Li-ion's 250 Wh/Kg. Similarly; Mg cells are expected to approach 1600 Wh/L versus Li-ion's 800 Wh/L. Moreover, magnesium is the eighth most abundant element on Earth, and is much less rare than lithium. At the same time, magnesium is easier and safer to handle and can be incorporated in cells using the same or similar manufacturing techniques as cells using lithium. An important class of problems in the development of all of these cells arises from inability to control the ongoing evolution of cell morphology and potential-distribution that occurs during charge-discharge cycles wherein electrochemically active species are redistributed throughout an electrochemical cell. In particular, anodes such as those employed in Mg, Pb, Li, and Zn-air cells can suffer from the development of non-uniform morphology during electrochemical cycling of the anode. Non-uniform morphologies variously referred to as dendrites, whiskers, asperities, and the like, can create immediately destructive and hazardous internal short circuits if they grow large enough to create an electrical connection between the electrodes of an electrochemical cell. This problem particularly plagues the cycle life of all metal-anode cells and, despite the potential benefits of metal electrodes, has led the industry to employ non-metal electrodes in many commonly used cell types to minimize these problems, even though non-metal electrodes do not completely eliminate these problems. Non-uniform morphologies also cause longer term capacity fade through two related processes: First, the creation of a high-surface-area interface between an electrode and electrolyte that forms massive amounts of decomposition products commonly-termed “solid electrolyte interphase” through parasitic, or unintended, reactions with the electrolyte. In the case of Li metal anodes, these side reactions of the electrolyte form “mossy Li deposits.” Second, the stripping cycle of the cell can leave finely divided, but electrically-isolated metal (known as the “dead lithium” problem in Li-metal technology development) distributed between the electrodes. Moreover, imbalances in the amount of active electrode material of the positive electrode relative to the amount of active electrode material in the negative electrode can also increase accumulations of undesirable metal or metal compounds. Consequently, rechargeable batteries can suffer such unfortunate events as thermal runaway, cell rupture, catching fire or even exploding if subjected to the wrong electrical or thermal conditions.
One approach, which is the dominant approach today, is to simply avoid the use of metallic electrodes altogether, by constructing electrodes operating as intercalation hosts, or alloying, conversion, and disproportionation reactions. This technique aims to eliminate a direct metal surface at the cost of energy density of the cell. Nevertheless, the use of intercalation hosts, or alloying, conversion, and disproportionation reaction materials results in a cell that may still ultimately deposit metal on an electrode surface under certain conditions of operation. Moreover, avoiding the use of metal anodes would very likely prohibit the implementation of Mg cells, now widely recognized as one of the most promising next-generation chemistries for moving beyond Li-ion batteries.
Another approach to preventing degradation of metallic electrodes has been to provide an ionically conductive, but electrically insulating coating such as a ceramic or polymer on the surface of the electrode that contacts the electrolyte. However, this approach will fail if even small imperfections in the coating exist, and the electrolyte can make direct contact with the electrode. Moreover, although there have been claims in the literature that certain coatings prevent surface plating, laboratory measurements presented below indicate that these claims are not reproducible, and surface plating that would lead to non-uniform morphological features occurs on the coating, obviating its utility.
The vast majority of electrochemical cells have only two electrodes: a cathode and an anode. However, a third passive “reference” electrode is well-known in the field and is widely used in both lab cells and commercial cells for monitoring purposes. These reference electrodes are managed so as to have no effect on the operation of the cell, and play no role in maintaining the performance of the cell. Since its role is to monitor cell electrochemistry, rather than to drive significant current, this reference electrode is generally much smaller than the two “working electrodes,” covering only a small portion of the active area of the cell. To limit any possible influence or interference with the working electrodes reference electrodes frequently lie outside the stack of cathode/separator/anode while maintaining ionic contact with the electrolyte. Similarly, in order to accurately measure cell performance without interacting with the working electrodes, the currents passed through a reference electrode typically lie in the range of 1-1000 ppm of the current through working electrodes.
In addition to the use of reference electrodes, there have been several proposals for third electrodes in the cell, several of which are discussed below.
Known in the prior art is Werth, U.S. Pat. No. 4,349,614, issued Sep. 14, 1982 (also published as European Patent Application Publication No. EP0060642 on Sep. 22, 1982), which is said to disclose an auxiliary electrode of platinum or palladium that is immersed in the electrolyte of a lead-acid battery and connected to the negative plate of the battery so that, when the battery is employed in float service, hydrogen evolves on the auxiliary electrode whereby the parasitic current equivalent to the hydrogen evolution increases the float current to the positive plate of the battery.
Also known in the prior art is Morris, U.S. Pat. No. 5,585,206, issued Dec. 17, 1996, which is said to disclose electrode sections, such as anode and cathode sections, of a battery cell that include current collectors with exposed portions. The exposed portions contain slits which form tabs. These tabs can be spot welded together to form connections between the electrode sections.
Also known in the prior art is Li et al., U.S. Pat. No. 5,688,614, issued Nov. 18, 1997, which is said to disclose an electrochemical cell provided with first and second electrodes, and a solid polymer electrolyte disposed therebetween. The electrodes may either be of the same or different materials and may be fabricated from ruthenium, iridium, cobalt, tungsten, vanadium, iron, molybdenum, halfnium, nickel, silver, zinc, and combinations thereof. The solid polymer electrolyte is in intimate contact with both the anode and the cathode, and is made from a polymeric support structure having dispersed therein an electrolyte active species. The polymer support structure is preferably a multi-layered support structure in which at least a first layer is fabricated of a polybenzimidazole, and at least a second layer is fabricated of, for example, poly vinyl alcohol.
Also known in the prior art is Maloizel, U.S. Pat. No. 6,002,239, issued Dec. 14, 1999, which is said to disclose a cell charging voltage adapter circuit, and a battery including such a circuit external to the cell and cell stack assembly, wherein the charging circuit includes terminals of resistor between one of the connecting terminals and one of the output terminals and a comparator between the connecting terminals and adapted to control the variable resistor in accordance with the results of comparing the voltage between the connecting terminals and a nominal voltage.
Also known in the prior art is Meissner, U.S. Pat. No. 6,335,115, issued Jan. 1, 2002, which is said to disclose secondary lithium-ion cells which include at least one lithium-intercalating, carbon-containing negative electrode, a nonaqueous lithium ion-conducting electrolyte and at least one lithium-intercalating positive electrode including a lithium-containing chalcogen compound of a transition metal, the electrodes being separated from one another by separators. A lithium-containing auxiliary electrode is disposed in the cell to compensate for the irreversible capacity loss in the secondary lithium-ion cell.
Also known in the prior art is Zhong, U.S. Pat. No. 6,383,675, issued May 7, 2002, which is said to disclose a third electrode for use in a metal-air tricell comprising a support structure coated with a layer of a lanthanum nickel compound and at least one metal mixture, wherein the mixture is adhered to the support structure without the use of an adhesive. In another embodiment, the Zhong invention relates to a metal-air tricell comprising: an air electrode; a metal electrode; and a third electrode, wherein the third electrode comprises a support structure coated with a mixture of a lanthanum nickel compound and at least one metal, wherein the mixture is adhered to the support structure without the use of an adhesive. Additionally, the Zhong invention also relates to a method of forming a third electrode for use in a metal-air tricell comprising the steps of: (A) applying a mixture of a lanthanum nickel compound and at least one metal oxide to a support structure, thereby yielding a coated support structure; and (B) heating the coated support structure in order to reduce the metal oxide present in the lanthanum nickel compound/metal oxide mixture to its corresponding metal and to adhere the mixture to the support structure, thereby yielding a third electrode wherein the third electrode is free of an adhesive.
Also known in the prior art is Slezak, U.S. Pat. No. 6,869,727 issued Mar. 22, 2005, which is said to disclose an electrochemical battery cell having a high electrode interfacial surface area to improve high rate discharge capacity, where the shapes of the electrodes facilitate the manufacture of cells of high quality and reliability at high speeds suitable for large scale production. The interfacial surfaces of the solid body electrodes have radially extending lobes that increase the interfacial surface area. The lobes do not have sharp corners, and the concave areas formed between the lobes are wide open, to facilitate assembly of the separator and insertion of the other electrode into the concave areas without leaving voids between the separator and either electrode.
Also known in the prior art is Wang et al., U.S. Patent Application Publication No. 2007/0141432 A1, published Jun. 21, 2007, which is said to disclose a third electrode frame structure for use in a fuel cell or battery is provided. The third electrode frame structure may include a first electrode, a separator positioned on an outer perimeter of the first electrode, and a frame third electrode coupled to the separator. The separator may be positioned in a same plane between the first electrode and the third frame electrode.
Also known in the prior art is Christensen et al., U.S. Pat. No. 7,846,571, issued Dec. 7, 2010, which is said to disclose a lithium-ion battery cell which includes at least two working electrodes, each including an active material, an inert material, an electrolyte and a current collector, a first separator region arranged between the at least two working electrodes to separate the at least two working electrodes so that none of the working electrodes are electronically connected within the cell, an auxiliary electrode including a lithium reservoir, and a second separator region arranged between the auxiliary electrode and the at least two working electrodes to separate the auxiliary electrode from the working electrodes so that none of the working electrodes is electronically connected to the auxiliary electrode within the cell.
Also known in the prior art is Roh et al., U.S. Patent Application Publication No. 2011/0217588 A1, published Sep. 8, 2011, which is said to disclose a secondary battery which includes an electrode assembly comprising inner stacked electrodes and at least one outermost electrode positioned on at least one end of the inner stacked electrodes; and a case configured to house the electrode assembly. The at least one outermost electrode comprises an inactive material.
Also known in the prior art are a range of techniques for the use of an additional electrode to monitor cell chemistry. For example, Kaneta et al., U.S. Pat. No. 8,017,260, issued Sep. 13, 2011, is said to disclose a secondary battery in which temperature rise (heat generation) can be measured accurately at the time of quick charge/discharge, and a battery which can be configured readily using the secondary batteries while realizing low resistance. Separately from the positive and negative electrode terminals of a flat laminate film secondary battery, a third terminal is fixed perpendicularly thereto. The third terminal is connected with the electrode current collecting parts of a power generating element body constituting the secondary battery (1) and imparted with a potential equal to that of any one of the positive and negative electrode terminals. Inner temperature of the secondary battery is determined by measuring the temperature of the third terminal and a cell balancer circuit, or the like, is connected with the third terminal. The battery is configured by connecting the positive and negative electrode terminals directly in series.
Also known in the prior art is Ramasubramanian et al., U.S. Pat. No. 8,119,269, issued Feb. 21, 2012, which is said to disclose three-dimensional secondary battery cells comprising an electrolyte, a cathode, an anode, and an auxiliary electrode. The cathode, the anode, and the auxiliary electrode have a surface in contact with the electrolyte. The anode and the cathode are electrolytically coupled. The auxiliary electrode is electrolytically coupled and electrically coupled to at least one of the anode or the cathode. According to Ramasubramanian, electrically coupled means directly or indirectly connected in series by wires, traces or other connecting elements. The average distance between the surface of the auxiliary electrode and the surface of the coupled cathode or the coupled anode is between about 1 micron and about 10,000 microns. According to Ramasubramanian, the average distance means the average of the shortest path for ion transfer from every point on the coupled cathode or anode to the auxiliary electrode.
Also known in the prior art is Roumi, U.S. Patent Application Publication No. 2013/0224632 A1, published Aug. 29, 2013, which is said to disclose separator systems for electrochemical systems providing electronic, mechanical and chemical properties useful for a variety of applications including electrochemical storage and conversion. Embodiments provide structural, physical and electrostatic attributes useful for managing and controlling dendrite formation and for improving the cycle life and rate capability of electrochemical cells including silicon anode based batteries, air cathode based batteries, redox flow batteries, solid electrolyte based systems, fuel cells, flow batteries and semisolid batteries. Disclosed separators include multilayer, porous geometries supporting excellent ion transport properties, providing a barrier to prevent dendrite initiated mechanical failure, shorting or thermal runaway, or providing improved electrode conductivity and improved electric field uniformity. Disclosed separators include composite solid electrolytes with supporting mesh or fiber systems providing solid electrolyte hardness and safety with supporting mesh or fiber toughness and long life required for thin solid electrolytes without fabrication pinholes or operationally created cracks.
Also known in the prior art is Noguchi, Korean Patent No. 1013754220000, issued Mar. 17, 2014, which claimed priority to Japanese Patent Application 2009/281122 through WO 2011/070712 A1, published on Jun. 16, 2011, which is said to disclose the following: Provided is a lithium-ion battery wherein internal short-circuits that are caused by inclusion of metallic foreign matter can be detected early with high sensitivity. Also provided is a method for producing the same. The lithium-ion battery, which is provided with a positive electrode (16), a negative electrode (15), and an electrolyte, is further provided with an electric insulating layer (3) which is between the positive electrode and the negative electrode and comprises an electro conductive layer (4). By applying a voltage between the positive electrode (16) and the electroconductive layer (4), and measuring a current and a potential difference between the positive electrode (16) and the electro conductive layer (4), the possibility of the occurrence of internal short-circuits in the lithium-ion battery can be detected early with high sensitivity since there is an earlier occurrence of a short-circuit between the positive electrode and the electroconductive layer than between the positive electrode and the negative electrode.
Also known in the prior art is Cui, et al., U.S. Patent Application Publication No. 2014/0329120 A1, published Nov. 6, 2014 (simultaneously with Cui, et al., WO 2014/179725 A1), which is said to disclose a battery that includes: 1) an anode; 2) a cathode; 3) a separator disposed between the anode and the cathode, wherein the separator includes at least one functional layer; and 4) a sensor connected to the at least one functional layer to monitor an internal state of the battery.
There is abundant recognition that the presence and the formation of non-uniform morphological features is one of the most serious problems in electrochemical cells, and particularly so in the compact batteries employed in devices such as mobile phones, grid-communication systems, distributed telemetry systems, tablet computers, laptop computers, backup-power systems, cameras, aerial drones, alarm systems, fire detection systems, personal fitness sensors, power tools, electronic instruments, musical instruments, aircraft, automobiles, satellites and many other devices with similar requirements. Unfortunately, there has been very little progress in managing non-uniform morphological features for such cells. Indeed, the primary driver for the adoption of intercalated electrodes is to suppress the formation of non-uniform morphological features, but the adoption of such electrodes comes at the cost of energy density.
In addition, it is well known in the field that non-uniform morphological features are a common failure mode even in cells utilizing intercalated electrodes. Specifically it is known that in Li-ion cells where the anode incorporates Li at a potential close to the Li metal-plating potential (including but not limited to anodes comprising graphite, silicon, or tin), non-uniform morphological features may form due to low-temperature cycling, excessive charging (either to too high potentials, or too rapidly) or a combination (see Adam Heller, The G. S. Yuasa-Boeing 787 Li-ion Battery: Test It at a Low Temperature and Keep It Warm in Flight, The Electrochemical Society Interface Summer 2013, page 35, Published online Mar. 25, 2013, for example). Thus the risk of non-uniform morphological features is known to be a prime limiter of performance in normal intercalation-anode Li-ion batteries, specifically limiting charging profiles, charging rates, and temperature windows for operation.
A more general description of some of the deleterious effects of deposition of metal or other material is that an anode electrode or cathode electrode can become distorted or changed in shape from the dimensions of the electrode that were originally provided in the battery, e.g., asperities or other changes resulting in non-uniform morphological features or dimensions of the electrode, can negatively impact the good operation of the battery.
There is a need for systems and methods that can control the undesired evolution of morphological changes of electrodes.